Currie’s 9-Plus for the Project Swinger Nova

“Curried” is an adjective that can apply to a huge range of different cuisine with an enormous list of ingredients – the only thing they have in common is that they’re all hot. So too, are the offerings on the menu from Currie Enterprises; they can build you a rear end in any configuration from mild to wild, using ingredients mixed and matched to meet your exact requirements.

Our project car, the Swinger Nova, recently received an upgrade to a Ford 9 inch rear end from Currie Enterprises. While the nine has been around forever in both stock and high-performance flavors, Currie’s recipes bring a fresh approach to this venerable axle. Follow along as we build a new Currie 9+ for our classic Muscle Car!

The Options

When it comes to building a Ford 9, your choices come down to either finding a used rear end from the wrecking yard and having it rebuilt, or getting a custom-built, completely new Ford 9 inch from an aftermarket manufacturer. Back when junkyard nines were plentiful and cheap, most of the time a rebuild was the least expensive choice, but now just finding a core to start with is getting more and more difficult.

After costing it out, a new complete rear end from Currie Enterprises was the smart choice for our project car. When you see the parts that are going in, and learn the history behind Currie, you’ll understand why.

Sizing a new Currie Axle at the factory.

About Currie Enterprises

Frank Currie began designing and building rear ends back in 1959, mainly working out of his garage, fabricating and assembling parts for specialty vehicles. Moving to a bigger facility in 1964, Currie Manufacturing of Placentia, California, turning their family off-road hobby into a full time business by developing aftermarket rearends for Jeeps. By the late 1970’s, Currie had branched out into the performance rear end market for V8’s and V8 conversion vehicles.

Rearends built on the Dana 60 and Chevy 12-Bolt were incorporated into the Currie product line in 1986. At that time, Currie Enterprises started designing and manufacturing complete custom-built 9-inch rearend assemblies, with nodular gear cases, alloy axles, and disc brakes in place of drums. Currie’s in-house capabilities grew and expanded, and today Currie Enterprises occupies a 27,000-square-foot complex in East Anaheim, California. Currie now has nearly 50 employees and boasts a state-of-the-art manufacturing facility where they design, build, modify, test, sell, and install rearend and drive-train products, all under one roof.

Removing the worn out GM 10 bolt from our classic street cruiser.

Picking out the right Currie rear end

Our Swinger Nova project car is shaping up to be a serious autocross and street cruiser. Because of the suspension and powerplant upgrades, it was crucial to get the engineers at Currie Enterprises involved in the rear end selection. Considering that we were upgrading to the Street Challenger suspension system from Air Ride Technologies, and adding a bit of muscle in the form of an LS3 from GM Performance, Brian Shephard from Currie recommended the Currie 9+ rear end package with custom mounting.

According to Brian, “More people are building higher-end cars and using more clean, brand-new pieces than ever before. Who wants to try and clean up a 40 year old rear end from the junkyard and have it rebuilt? By the time you’re done with that, you’re into it for about two grand.” We took a hard look at the pricing, and we were pleasantly surprised to find that a custom-built rear end from Currie was about the same cost as rebuilding a stock rear end from the wrecking yard. As an added bonus, the Currie rear end has a major improvement in strength. Brian explained that using the nodular iron third member case instead of the stock gray iron improved the strength of the material from 25,000 PSI to 65,000 PSI.

The choice to use the Currie 9+ rear end over a refurbished stock piece was a no-brainer in every aspect. Economically and functionally, we were sold on getting a 100% all-new unit that is custom built to our specs and can handle “600 horsepower without breaking a sweat,” as Brian said.

Custom Specifications – Currie 9+ Rearend

  • Housing: Currie 9+ heavy duty round-back housing with GM multi-leaf mounting pads
  • Axle Tubes: .188-inch wall thickness, 3-inch diameter with late-style large bearing ends (Torino bearings)
  • Axle Shafts: High performance axle package with 31-spline, 2.8-inch diameter axles. 27.5-inch driver’s side and 31-inch passenger side length
  • Retainers: 1/4-inch heavy steel
  • Bolt Pattern: 5 X 4 3/4-inch
  • Third Member: Cast nodular iron case with Daytona-style pinion supports and 1350-style 65,000 psi nodular cast iron yoke
  • Differential: 31-spline Detroit TrueTrac worm gear limited slip unit, 3.70:1 ring and pinion gears

The Nuts and Bolts

The Currie rear end housing we’re using (part number CE-2001N) is a completely new stamped heavy-duty housing center featuring a standard 23-inch wide ‘round back’ style rear cover. The axle tubes are a sturdy three-inch diameter, .188 inch wall thickness D.O.M. tube. The housing has a close-fit 7-inch deep socket for positioning of the axle tubes. The “fish mouth” sockets are reinforced with internal gussets to assure precision alignment and maximum strength.

On the axle tube ends we requested late-style large bearing ends (Ford Torino type). The housing, as with all 9-inch housings in this line, was custom built and MIG welded to our specifications. With driver’s side tube width almost 22 inches and passenger’s side tube at 22 and a half inches, the overall width ended up exactly at 60 inches when assembled with axles. We had the pinion offset built in at half an inch. To finish off the deal, the housing came with third member studs installed, and the third member gasket, nuts and washers included.

Unpacking the parts.

Down for the Count?

The axle package we selected (part number CE-0012) is intended for high performance applications, with a 31 spline count and 7/16-inch wheel studs. The axle shafts themselves measure out at 2.8 inches in diameter with the drivers axle just shy of 27.5 inches and the passenger’s side axle at almost 31 inches. The axle hub face diameter measures at 6.250 inches, the axles are retained by a quarter-inch thick heavy steel plate, and they will accept any aftermarket brakes that fit a Ford 9-inch rear end. We chose to get a lug pattern of 5 on 4.75 inches on the axle hubs. Currie offers axle packages that include 30, 33 or 35 splines and lug patterns up to a whopping 6 on 5.5 inch for truck applications.

Currie’s cast nodular iron case and 31-spline, limited slip differential with 3.70:1 ring and pinion gears.

Members Only

This is where the Currie rear end really gets spicy. The new cast third member case (part number CE-4026C) is cast from extra-strength nodular iron and precision machined to original O.E.M. specifications. It is a “brand new” manufactured unit, not a salvage yard rebuild. The case is set up just like a stock 9-inch gear case, and every 9+ provides ideal gear tooth contact between the ring and pinion. The OEM case flexes under heavy loads and extreme conditions. This causes the ring and pinion to shift in relation to each other, resulting in premature wear, binding, and failure.

Installing the third member into the 9+ housing.

The differential we selected was a 31-spline Detroit TrueTrac worm-gear style limited-slip unit with a 1350-series yoke attached to the pinion gear. The 1350 yoke is also cast out of 65,000 PSI nodular iron, and is designed for use with ‘big bearing’ pinion supports. These ‘Daytona’ type pinion supports have larger ribbing and are inherently stronger than stock-style supports.

Tightening down the third member.

We opted to go with Currie’s 3.70:1 ratio ring and pinion gears. With the LS3 engine, we should be able to turn these gears as fast as we want and get through a series of tight turns without dropping the revs. The TrueTrac will get power to the wheels on demand without fear of breaking the high tensile strength 31-spline axles.

Currie’s representative Brian Shephard explained that the concept behind this sportsman line of rear ends was simple. “With the diminishing availability and problems trying to match rearend components, our solution was to redesign and build the better Ford 9-inch parts, make them affordable, and offer a comprehensive line of matched components.”

Hauling the Freight

The Currie rear end comes un-assembled, and that’s largely due to freight charges. You can get an entire rear end assembled at the factory if you want, but expect to pay more for the freight. The real savings in buying a Curry rear end is that it is pretty much a modular assembly. You can easily upgrade or change parts because all the components are designed to work together. If you want to change out the gears in your rear end, it’s simply a matter of changing out third members. You can order any piece of the rear end and expect it anywhere from 3-5 days later.

One of the great things about the Ford 9-inch is the fact that the critical relationship between the ring and pinion is maintained by the third member, instead of the axle housing. That means that the gears can be professionally set up in the third member and shipped separately, then assembled by the end user without any tedious precision work required.

Putting it all together

Putting the Currie rear end assembly together is fairly easy and straightforward once you have the components removed from the boxes. Start by placing the housing on a rear end stand or bench. The work area needs to be stable and strong enough to support the weight of the entire rearend assembly once it’s complete.

Using high temperature RTV black silicone, run a thick bead of sealer around the mating surface of the axle housing, making sure to run a bead of sealer all the way around the studs. Install the third member and torque the bolts to 30 ft/lbs. Install the axles and retainer plates. Test the TrueTrac locker by turning one of the axles. The opposing axle should spin in the same direction if the locker is functioning properly. The rear end can then be installed into the chassis.

Raising the new rear end to the chassis.

Wrapping it Up

Using a tranny jack to support the rear end, and with the car on a two-post lift, we raised the Currie rearend into position. A quick attachment of the Air Ride ShockWave shocks and the upper and lower control arms from the Air Ride four-link cradle to the rear end and the new 9-inch was in place. Using an angle finder, we adjusted the length of the lower links so that the pinion was at 2 degrees nose-down.

Installing the SSBC rotor onto our new Currie 9+ rear end. A big rotor for a big axle hub.

Now that we had the rearend installed, the brake hardware could be hooked up, the calipers installed, and the tires fitted on the hubs. By ordering from Currie, we had the confidence that comes with all-new parts, and instead of having to make due with what we could find in a junkyard, we had a housing that was made to our exact specifications by some of the most experienced people in the business.

Currie also saved us a lot of brow sweat by putting together the right axles, third member, differential, and gears for our project – getting just what we needed for the Swinger was literally the work of a single phone call. When the parts arrived, everything went together right the first time and bolted straight up to our Nova with no fabrication or tweaking required on our part. We had the best of both worlds – a brand new custom 9-inch rear end, with off the shelf pricing and convenience.

Our project car back down on the ground, waiting for tires and rims.

Article Sources

About the author

Bobby Kimbrough

Bobby grew up in the heart of Illinois, becoming an avid dirt track race fan which has developed into a life long passion. Taking a break from the Midwest dirt tracks to fight evil doers in the world, he completed a full 21 year career in the Marine Corps.
Read My Articles

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